Goliath
Gantry Cranes
Their Steel Structure – A Neglected Element
Experiences in Surveillance and Reconditioning
of the Last Two Decades
Vladimir Nevsimal-Weidenhoffer[1]
Intercrane Pte. Ltd,
Assoc. Prof. Nicholas G. Tsouvalis[2]
and Prof. Vassilios J. Papazoglou[3]
1. INTRODUCTION
Goliath gantry cranes have been increasingly
used in the shipbuilding industry for up to five decades, their size and
lifting capacity becoming larger as the size of ships and their building blocks
increased. Existing designs of these
very large metallic structures currently offered by the crane manufacturers can
have a lifting capacity of up to 1500 tons, lifting height between 50 and 115 m
and a rail span of up to 210 m. Many of
these cranes have been built during the 60’s and 70’s and they are approaching the
end of their nominal design life. The aim
of this paper is to demonstrate that while steel structures of Goliath cranes may
over their lifetime carry a somewhat divergent kind of risks, these risks, by
their nature, may be quite significant with potential consequences far larger
than those applicable to other cranes. The
authors, having an extensive experience in the investigation, repair, refurbishment
and development of Goliath cranes (see Appendices 1 and 2), are aware that the general
topic applies to all cranes; however, to illustrate the problem, this type of
crane was chosen because:
-
the
ratio of the structural component to other components of the crane is the
highest in these cranes,
-
general
opinion of the corresponding industry (assisted, no doubt, by difficult and
often dangerous access conditions), rates steel structure of these cranes as
least susceptible to potential problems.
Three types of service are usually applied on a
Goliath crane structure during its lifetime, in periods superimposed on each
other. These are:
(i) Maintenance
(ii) Reconditioning or refurbishment
(iii) Enhancement of technical/operational life
The first type of service, which
lasts over the entire life of the structure, is not subject of this paper. The
second, commencing at about 20-25 years of age (depending on the rate of utilization
as well as on quality of maintenance) is applicable for approximately 15 years,
superimposed on the first. Structural refurbishment
is usually being performed in conjunction with renewal of electrical (technology
progress or lack of spare parts) and mechanical (renewal of gears, brakes,
bearings, etc.) equipment of the crane. Timing
of structural refurbishment is no hazard; it is at this time that first defects
start showing through the paint (more about the origin of these defects in
section 4). It takes all this time
(20-25 years of operation) for the various defects of the steel structure (i.e.
cracks) to grow enough to work themselves through the current elastic
protective coating systems.
Normally structural refurbishment
should conveniently coincide with renewal of the protective coating, but there
are other dominant constraints such as loss of production and cost, that
influence such decision. Most certainly,
it would be a logical step to include renewal of protective coating into this
period and, additionally, let the inspection benefit from the exposed blank
metal of the structure after the necessary blasting. Regrettably, such an approach is not usually
followed by the yards, who normally do not subordinate the time requirements of
painting to the legitimate and important needs of parallel structural inspection,
irrespective of how sensible such a course of action may be.
The third service type during the
lifetime of a crane structure involves interventions that, while in progress
over several years, are still in an exploration and experience-collecting
stage. To the best of the authors’ knowledge,
in this category of cranes only one project of this kind has been attempted and,
while in its final stages, it is still in progress. However, technical feasibility and cost attractiveness
of this project have already been proven beyond doubt. Current knowledge on the subject is described
in section 6.
2. inspection
Before dealing with the inspection
procedure, requirements to carry it out should first be examined. To commence with, the most important part is
the inspector. He must possess
engineering qualifications (preferably in several fields) as well as experience,
the latter being of primary importance. Physical
fitness, tolerance of dirt, bruises, inclement weather and, above all, easy adaptation
to work in height and in confined spaces, are equally a must. Briefly, inspection is work for professionals
and that for professionals of a “trench type”.
Another primary requirement is
good and safe access. This is not a small
problem, given the fact that the structures are very large along all three dimensions
and that many areas of interest are in locations with difficult access
conditions. Mobile or fixed scaffolding,
hydraulic platforms or platforms suspended from nearby jib cranes or even from hired
telescopic cranes are most often used.
However, it should be emphasized that not all of these practices can at
all circumstances comply with the most stringent rules of safety codes. There is always an inevitable factor of risk
in every inspection and it is the duty of the inspecting team to minimize this
risk as much as possible.
Regarding the inspection and its
objectives, what an inspector should primarily look for are the consequences
of:
-
Material
defects
-
Design
errors or omissions
-
Fabrication
defects
-
Erection
defects
-
Corrosion
-
Operational
damage
-
Unauthorized
interventions, and
-
“Ghost”
items
The unusual last term is used to represent situations
impossible to be anticipated, even to be imagined. For better understanding, relevant examples
will be discussed in section 4.
Having established what an
inspector should look for, let us turn to how to localize these items or, in
broader terms, which are the areas of interest through the crane structure. However, prior emphasis should be given to
the obvious and self-evident principle that for all practical purposes it is impossible
to locate and identify all defects on a structure. On the other hand, the duty of the inspector is
to localize and identify ideally all defects of importance, in particular those
that could present a threat to structural integrity.
A good starting point is review of
structural drawings and calculations, if available. Although of limited help, such a review is
always useful even if drawings alone cannot reveal complete picture of potential
problem areas; moreover, availability of “as-built” drawings is rare in most
instances.
Turning from general points to visual
inspection, a skilled engineer is able to anticipate potential problem areas,
but after that it is experience that takes over. However, experience alone is equally
insufficient, since it will always be limited by the past, e.g. it is only what
you experienced in the past you can anticipate in future. The inspector should always keep in mind that
protective coating is providing the best “cover-up” and defects are not always evident. Generally speaking, a proper visual
inspection should always, right from the start, include a sound and well planned
approach concept, a good eye, attention to detail and intuition. In addition, understanding and correct
interpretation of some “signs” of damage, in conjunction with an inductive
reasoning regarding the way the structure is operating, can lead the inspector
to localization of further areas of interest.
Non-destructive investigation techniques
are normally incorporated in these inspection procedures, but being intimately and
widely known, in this paragraph emphasis is given only to their limitations. First of all, the cost of these techniques and
the required time to be spent on the structure are two major factors that have
to be considered. In addition, cost of
access required must be taken into account, not forgetting that many of these
techniques require special conditions (e.g. absence of paint, optimum weather,
etc.) that further limit their use. All
of these factors together speak by themselves against massive application of
non-destructive investigation techniques (the only exception perhaps being the Alternating
Current Field Measurements – ACFM). Due
to the above reasons, the role of these techniques is normally restricted, mostly
towards verification of areas of interest defined previously by visual
inspection. In these cases they can be
very useful, even indispensable. Under
such conditions, even a multi-layered NDT approach can be required and applied
to the best effect. In conclusion, in an
inspection non-destructive investigation techniques will always remain a useful
support tool of an overall effort carried out by other means.
In summary it can be stated that
inspection is the most important element in condition monitoring, refurbishment
and life-enhancement service periods, providing an information basis for any one
of these service types. Its quality is of
paramount importance for success of these services, whereas its grading,
accuracy and assessments based on it largely depending on the individual in
charge.
3. REFURBISHMENT
Based on results of preceding
in-depth inspection, refurbishment represents the first stage in reconditioning
of a structure during its lifetime. In
the true sense of the word, its objective is to improve overall condition of
the structure bringing it as close to its original status as possible. As previously indicated, it can be (and often
is) combined with other major interventions, such as:
-
modification
of the crane (e.g. geometry, capacity, performance)
-
modernization
(e.g. electrical equipment)
-
transfer
of the crane to other location
While the above interventions are of equal interest
with the refurbishment works, dealing with all their aspects, requirements and
special conditions is clearly beyond the scope of the present paper; hence, we
concentrate further on refurbishment of the structure.
Based on results of inspection,
priorities of work are established and, unless immediate interventions are required
before crane operations can be resumed, the schedule of works is fixed, always depending on crane availability. This is the first and crucial parameter that
will rule execution of works. Its
importance is witnessed by the fact that the way of execution of a given
corrective measure is often dictated by requirements of the production
department of the yard and consequent availability of the crane.
The second and equally crucial parameter
is weather conditions (temperature,
wind, rain) permitting satisfactory and safe execution of works. Moreover, final two major parameters to consider
are the conditions of access and,
last but not least, the cost.
Taking into account all the above
parameters, refurbishment works can be split-up into the following categories:
a) Works where
prior engineering is not required, with easy conditions of access:
In such case everything is a matter
of labour. Experience
has shown that best results have always been achieved by using workforce of the
yard. There are many advantages in this approach; the people are motivated by
working on their own equipment and are much more efficient instantaneously knowing
the whereabouts of any services, tools or other support. An additional benefit to the yard and to each
one of the staff involved is that by working with the inspecting team they acquire
some experience in detecting, analyzing and repairing structural defects on
their own. Thus the yard is acquiring a measure
of know-how and that free-of-charge! Of
course, reasons for using the workforce of the yard are equally valid in the
case of the next two categories of refurbishment works.
b) Works where prior engineering is required:
Engineering solutions are
generally provided by the inspecting team and the yard may wish to participate
in this procedure. In all cases, design of
these solutions should respect crane availability and lifting requirements. The inspecting team also carries out various special
investigations and tests (i.e. advanced structural analysis, laboratory material
examination tests, etc.), if and when required and to the extent the team is in
possession of means for doing so. Otherwise, such services are subcontracted, the
inspecting team having the supervision. The same applies to supply of any
hardware required by the engineering solution.
c) Works requiring special access arrangements
and/or heavy lift operations:
Although actual refurbishment
works remain the sole responsibility of the inspecting team, tasks like
creation of the necessary infrastructure for carrying out this type of works
(i.e. scaffolding, erection, bringing down for dismantling, review and refurbishment)
are generally subcontracted, but their planning would always remain subject to approval
of the inspecting team.
Regarding defects that
can be encountered during an inspection, some characteristic examples are presented
and analyzed in the next section 4. As
far as their origins are concerned, an indicative list was given in section 2,
but their split-up is impossible to quantify; there is no general rule.
Corrosion is, of course, of frequent
appearance on these structures and its origins are not to be sought primarily in
poor design; negligence in conservation is mostly the cause. Corrosion is capable of creating dangerous
situations on its own, particularly if of the hidden type.
Renewal of protective coating in
parallel to refurbishment works has already been mentioned in section 1. However it should be emphasized once more that,
apart from its protective role, protective coating can equally cover up a
number of actual or potential problems.
Last, but not least, the issue of
damage. It is quite natural that in real
life every crane is virtually bound to suffer some damage from operations. As such damage may have serious consequences,
it is imperative that it does not go unreported. Staff that directly witnesses such accidental
damage is, in the majority of cases, not qualified to assess its importance. Moreover, human nature tends to hush up such
incidents and leave the situation as it is.
It is therefore warmly recommended to encourage staff to report every accidental damage and leave the
decision on its importance to those with relevant qualifications. Crane drivers in particular should be
encouraged in this direction as, under circumstances, their lives may depend on
it.
Finally, equal emphasis should be
given to the issue of damage caused by unauthorized and/or inappropriate
interventions. Welding, drilling,
oxy-cutting etc. without previous proper consideration and supervision can
result in considerable damage, which is often uneasy, if not impossible, to
repair. Approval, insistence on
discipline and proper supervision in all interventions is therefore a clear
must.
4. Defects
Regarding defects that can exist
on the steel structure of a Goliath crane, the most common categorization is
linking the defects to their origin.
Thus, as mentioned in section 2, defects can be subdivided into several
major categories, such as material defects, i.e. defects having their origin in
production of steel and of steel products; design errors or omissions having
their origin either in oversight during design or in lack of sophisticated
design tools, like modern finite element software codes; fabrication and
erection defects created during these two stages of the crane construction,
having their origin in poor workmanship or insufficient supervision; corrosion
problems caused by either poor design or improper maintenance; operational
damage, most often caused by collisions with surrounding structures or
equipment; unauthorized interventions in the structure by inexperienced
personnel; and finally “ghost’ or
“phantom” items, a general category including all cases hard to imagine,
usually as a result of a combination of all the above parameters and beyond. Typical examples of those defects encountered
by the authors are shown below:
4.1
Material defects – Case 1
This case refers to a defect
discovered in the lower part of web of the main beam of a large gantry crane,
near the joint with the bottom flange (see Figure 1). It existed at mid-span, extending for a
length of approx. 600 mm and a height of 50 mm above the bottom flange. It was discovered by the Alternating Current
Field Measurement (ACFM) method. First
it had appearance of a crack, but after careful examination and grinding it was
established that it was a “lap” in the plate, present since the origin that after
the years became loose. Careful grinding
of the area was carried out until the defect was eliminated. No re-welding was envisaged due to tensile stress
permanently present in this area from the main beam own weight, reaching approximately
100 MPa.
Figure 1: Material defects – Case 1.
4.2 Design errors – Case 1
The design problem in this case
was a cable hole in the bottom flange of a cross beam of the crane, being
oriented with its largest dimension perpendicular to the direction of principal
tensile stresses developed in the plate (see Figure 2a, where half of the cross
beam is shown for better illustration).
This configuration resulted in a large stress concentration at the edges
of the hole, which in time could have jeopardized structural integrity of the
cross beam. The area was reinforced by
putting friction-bolted doubler plates near the edges of the cable hole. Various shapes were investigated by using
finite elements, with the one shown in Figure 2b found to be the optimum one.
(a) (b)
Figure 2: Design errors – Case 1.
4.3 Design
errors – Case 2
The problem was the existence of
an undercut in a junction of bottom flanges of two beams of a trolley (Figure 3a),
both these flanges being loaded in tension.
Repair works included filling of the undercut with weld and welding of
an additional curved bracket, as shown in Figure 3b). The initial right-angle corners of the
bracket were, after welding of bracket to the beams, ground smooth for optimum
geometry.
(a) (b)
Figure 3: Design errors – Case 2.
4.4 Fabrication
defects – Case 1
In this case, the problem
concerned improper execution of throat weld between the top flange and the web
of main beam of the crane, just below the trolley rail (Figure 4). Insufficient penetration of this welding
resulted in development of a longitudinal crack in the weld extending for about
200 mm, discovered by the ACFM method. The crack was repaired by careful removal and
rewelding limited to the area where the crack was found. Although the problematic throat weld was
extending along the whole length of the section involved (16 m), for practical
reasons it was not possible to repair the whole weld. The yard was informed to pay specific
attention to this area during future surveys.
Figure 4: Fabrication defects – Case 1.
4.5 Fabrication
defects – Case 2
In many cases, remnants of gussets and
brackets used for fabrication and/or erection purposes were found like those
shown in Figure 5 below. These remnants
were traces of weld metal due to improper removal of these structural
appendices leading to cracks in some cases.
The cracks were discovered by grinding out these remnants and
investigating the area with NDT techniques.
Repair was limited to grinding out the cracks, since they were not deep.
Figure 5: Fabrication defects – Case 2,
two different examples.
4.6 Fabrication defects – Case 3
A common fabrication defect is poor
quality of edge cutting of various free edge plates, like the one shown in
Figure 6 of the cross beam web plating.
These saw-tooth shaped edges are a perfect example of potential crack
initiation points, when they are parallel to main tensile stresses of the
structure. The problem was resolved by
grinding the edges smooth and checking with magnetic particles to verify that
no micro-cracks remained behind.
Figure 6: Fabrication defects – Case 3.
4.7 Erection defects – Case 1
This case is about a situation on
the main beam of a Goliath crane equipped with a bracket. In the area of maximum tensile stress of the
beam top flange, lifting plates for erection purposes were introduced passing
through the tension flange in a direction perpendicular to the principal stress
(Figure 7). After erection these plates
were cut off flush with the top surface of the flange. The erector, being aware of having done
something incorrect, drilled a hole on each side of the slotted plate,
introducing a bolt in each, spot-welded to the flange. In addition, a reinforcing plate was designed
and welded to the flange on each side of the detail (Figure 7). The result was creation of cracks in the bolt
holes, with much worse potential damage to be expected from such
arrangement. Repair included removal of
existing reinforcing plates and designing and installing friction-grip bolted
doubler plates on both sides of the flange, around the critical area.
Figure 7: Erection defects – Case 1.
4.8 Erection
defects – Case 2
This example concerns bolt holes drilled
initially to accommodate bolting of connection plates in order to join by
welding sections of the crane beam.
After assembly, these holes were normally filled in by welding. In several cases, this welding was done improperly
resulting in formation of defects like those shown in Figure 8, leading to
severe stress concentrations. These
defects were visually discovered after removal of paint. Initial attempt to re-weld the holes with
preheat led to formation of cracks. This
fact indicated that the parent material was very brittle, indicating execution
of the initial fill-in welds at a low temperature and without preheat. Final solution was to re-drill the holes,
preheat and re-weld.
Figure 8: Erection defects – Case 2.
4.9 Erection
defects – Case 3
This case refers to the damage done
to the service crane rails in order to fit the power tool socket on the bolt
head to torque up the bolts. The bottom
of the rail head was oxy-cut to make more space for the socket, as can be seen
in Figure 9. No corrective measures were
taken in this case, as the damage was characterized as irreparable. It has to be noted that these rails,
friction-grip bolted to the main beam (hence part of the cross-section) are
located in a zone of maximum tensile stress of the top flange, due to bracket
action mentioned in paragraph 4.7.
Figure 9: Erection defects – Case 3.
4.10 Corrosion – Case 1
As shown in Figure 10, extensive
corrosion was discovered at a friction-grip bolted joint of the main beam, due
to insufficient attention paid to the water tightness of this joint. Corrective measures consisted of removal of rust
as much as possible and sealing the joint.
Figure 10: Corrosion –
Case 1.
4.11
Operational damage – Case 1
This example involves damage to
one of the main beam webs near the counterweight area, due to collision with another
crane (Figure 11). Compressive strength of
the web plating has been substantially reduced by this damage. Repair was done by reinforcing local
stability of the structure by installing additional stiffeners inside.
Figure 11: Operational damage
– Case 1.
4.12
Unauthorized interventions – Case 1
A perfect example of this
category of defects is the case of an equalizer, where a bracket was initially
welded to its bottom flange (probably as a temporary measure to support it) and
then cut-off. As a result, remnants of
the weld including undercuts were left in the flange. These remnants were ground out and consequent
NDT check showed no cracks. However,
grinding resulted in a significant local reduction of the flange
thickness. Since the equalizer flange
was subject to considerable tensile stress, a weld repair procedure was
proposed to the owner, who declined execution.
4.13
“Ghost” items – Case 1
This case involves holes which
were initially drilled to accommodate fitted bolts of a joint. Since installation of these was found
expensive by the erection company, the fitted bolts were replaced by HSFG bolts
(having diameter smaller by 1.2 mm) and these were torqued up. Problem:
the erection company “forgot” to properly prepare friction surfaces by
blasting, leaving these surfaces with a coat of primer, as initially prepared
for the fitted bolt connection.
4.14
“Ghost” items – Case 2
The next case involves again a
bolted connection equipped with fitted bolts.
Several years after the erection of the crane an inspection company of
some renown “found” that these bolts were not torqued up, believing wrongly
that they had in front of them a friction-grip connection. So they torqued up the bolts that, although
of 8.8 grade, did not have the geometry to withstand these stresses
undamaged. Result: all of these bolts when removed showed cracks
in the thread-shank intersection.
4.15
“Ghost” items – Case 3
This example refers to the lower
horizontal box girder of a triangular shear leg of a crane (Figure 12). The box girder had an approximate width of
800 mm and a height of 600 mm and was of the fully seal-welded type, e.g. there
was no access into the interior. A cable
tray was running on top of this box girder, sitting on “buckles” welded to the
top flange. These buckles were so low
(30 mm) that it was impossible to look properly under the tray.
The first indication was that the
zone under the cable tray was heavily corroded.
After removal of the cable tray and cleaning of the rust underneath,
five small holes were discovered with a diameter of approx. 6 to 8 mm in the
zone under the tray, in a rather concentrated area. A wire test established that they were going
through the thickness of the flange.
These holes must have been drilled before installation of the tray,
which, evidently, was never removed before.
Result of these holes was water
penetration inside the box beam, a fact that remained unknown for 30
years. The beam had no protective
coating on the inside and, in consequence, heavy corrosion has formed. The box beam was opened on the side and about
50 buckets of rust mud were removed. The
thickness reduction of the plates was about 50% in the bottom flange, 30% in
the webs and 20% in the top flange. The
only favorable issue was that the holes were very small, their diameter further
reduced by rust. As a result, water and oxygen
penetration remained restricted.
In order to fix the problem of
the box beam under permanent tension, it was recommended to use reinforcing
strips in the areas affected.
Figure 12: “Ghost” items –
Case 3.
5. Regular inspections AND their importance
It is evident that at all times the
structure must remain under surveillance, especially after refurbishment. This, not only to safeguard its safety and
integrity and verify correctness and adequacy of the measures taken, but
equally as a wise cost-cutting measure.
Current codes[4],[5]
are relatively vague on the subject of intervals between these inspections and,
in view of the authors, this is because there are many factors influencing a decision
like this, such as:
-
initial
condition of the crane on delivery (design, fabrication, erection)
-
quality
and frequency of maintenance works
-
rate
of exploitation
-
climatic
conditions (corrosion rate)
-
damages
etc.
-
and,
inevitably, the cost factor
In this context, a question may
be raised whether it is better to have these inspections carried out by
different inspectors, or whether it is of advantage to keep them in the same
hands. While the first approach may
bring the benefit of difference in view-points and experiences, it is the
latter option that is favored and recommended.
The first reason for this recommendation is that knowledge of case
histories of individual defects by a single inspector is of considerable
advantage, an advantage that must not be lost.
The second reason is that, only that way, a long-term “relationship”
with a structure can develop and result in a “feel” for it.
Under such
conditions a decision on frequency, even extent of inspections, is easy and
optimized. In any circumstances, a
decision on these issues should be left in the hands of an expert, rather than
to rely on some inflexible rules that may (and in many cases do) either
underrate or overrate the issue, resulting in losses either in safety or in
cost.
6. Enhancement of operational life
Aging is a natural process of all
things, bringing their life to end at some stage. However, within this fact it is necessary to
distinguish between “life” and “useful life”, the end of which may come much
earlier. Leaving for the moment all technical
aspects aside, the extent of useful or operational life of a Goliath crane
depends on:
-
adequate
compatibility with operational requirements at a given time, and
-
cost
of operations
If the first point can be
anticipated satisfied over an extended period of time, then it is of interest
to examine the option of enhancement of operational life of a given crane structure.
The first condition to be satisfied is the
economy of such action, i.e. the ratio between the cost involved and the
additional number of years in operation so gained. A further condition is reasonable (restricted)
maintenance cost during the time so gained.
Nowadays the prevailing view of
the industry is that the currently operating generation of Goliath gantry cranes
(built in the 60’s and afterwards) has a very long life. This belief is essentially correct, although it
is still not exactly known how long is “long”.
There is indeed a large variety of software available for residual life
calculations that can be used in an estimate of the life of the structure. The question is, of course, how reliable
results of these calculations are, the problem not being associated with the
validity of the software codes themselves, but mostly with the way these codes
are implemented in a structure as large and complicated as a Goliath gantry crane. Such calculations will readily show how long a
theoretical model of the structure can last until the limit number of cycles of
a critical member is reached. However,
this result will be on the basis of an ideal configuration, where very few of the
problems inflicted on the real structure during and after its conception can be
modeled. Hence, whatever may be established on the basis of a theoretical
calculation, it will be nothing more and nothing less than an upper boundary of
the residual life of the crane.
Moreover, a definition has to be
given to what residual life really means. The answer to this can only be the useful
(operational) life of the structure, within the above mentioned maintenance
cost limitations, since any other definition has no practical value. As far as “life” is concerned, the current
status is that inspectors are still in the process of gathering experience and
for this reason the answer to the all important
question “how long?” remains inconclusive for the time being.
Having established
what “life” of a structure means, here we arrive at the fundamental difference
between refurbishment and enhancement of operational life, be it in the technical
measures to implement or in their costing.
In the first case (refurbishment),
after a thorough inspection the inspector knows virtually all and it only
remains to add it up. In the second case
the issue is practically the same, but this is only the starting point. Major part of “enhancement of operational
life” works consists, firstly of correctly
anticipating one or more sequences of local deteriorations that could
potentially lead to local failures, and thereafter, of developing and implementing
measures how to counter these in time. This
involves a combination of surveillance with preventive engineering measures,
ranging from improvements over to modifications and even complete replacement
of components; all these, of course, under constant review of cost to keep this
important factor in check.
All in all, “enhancement of
operational life” is a task of constantly keeping ahead of problems before they
develop or, at least, before they become unmanageable and this at cost levels
that can be justified at all times. No
doubt a daunting task, but it can be done successfully as the authors’ engagement
of the last six years demonstrates. Additional
experience from current and future projects shall refine the tasks of this kind,
improve their technical and financial success and, in consequence, add to their
attractiveness to the industry.
7. OVERLOAD
TESTS
Following reconditioning measures
discussed in chapters 3 and 6 it is sometimes necessary to subject the crane,
or part of it, to an overload test.
To evaluate its full effect on a
structure is a complex issue transcending scope of this paper.
Nevertheless, the authors feel
the need of proposing at least some principal guidelines for such tests:
1. During its lifetime the crane suffers unavoidable damage
(accidents, unauthorized interventions, corrosion) and consequences of any
weakness in design, fabrication and erection.
In other words, as the years pass the structure accumulates problems
which with each new test may grow, thus increasing potential risk.
2. These tests represent the most damaging condition for
the structure and, as such, they should remain very limited in number during
lifetime of the crane. They should not be carried out unless fully justified on
technical grounds (crane age and problems known taken into account) and, if so,
should include good planning to limit potential risks and a good check-out on completion.
3. While overload tests constitute the only method of
exhaustive evaluation of effective operational security, they do NOT represent
a guarantee against failure on their own.
Only in conjunction with close monitoring of the crane (ref. chapters 2
and 5) the desired levels of safety can be attained and maintained.
8. Conclusions
This paper presented fundamental
steps in taking care of a steel structure of a Goliath gantry crane, including
problems to be expected and principles of how to deal with them. By doing so, the aim was to dispel some widely
established myths still pervading the industry, namely that:
-
steel
structures of Goliath gantry cranes require only a minimum amount of inspection
because they are largely “inert” to risks, and
-
steel
structures of such cranes do not, in general, suffer from fatigue.
Regarding the first point, the
previous sections of this paper demonstrated beyond doubt that the situation is
different and that structural components of these cranes need at least as much
attention as those of any other crane, in particular given the magnitude of
potential risks involved. And here we
are not talking only about magnitude and value of such crane, hence of
potential cost of major technical problem.
Far more important appear specific consequences of such problem for
operations. For, contrary to other crane
equipment, many of these cranes operate over a dock as a single unit offering little
or no possibility of rapid substitution by another crane. In case of their immobilization, lost
production not only means disruption and delays, but far too often painful
financial losses for the construction process of the yard.
As far the
second item is concerned, it should be clearly stated that this point of view
is as much in error as the first one. The
answer to the question “in what part of the crane, if any, fatigue damage can
evolve”, the response is “in those areas where the number of cycles required for
fatigue to develop can be collected”. In
a frequently used crane, such areas should particularly be sought in the
long-travel system exposed to imperfections of the track and inertial forces
from travel.
The very essential at the end:
All the works mentioned can only be carried out and completed successfully on
condition of first-class cooperation between the parties; hence in full mutual
confidence, trust and respect of each party responsibilities. Where these conditions do not prevail, works
should be terminated at once as their continuation may result in unacceptable
risk to this or that party, or both, and, most importantly, to the safety of
the equipment and of those operating it.
APPENDIX 1
Experience in refurbishment/repair and development of
heavy gantry (“Goliath”) cranes
(Depicting the name and location of the client, the
participating companies,
the general characteristics of the object and details
of activities)
1989-90 : Burmeister & Wain/Copenhagen
/ Denmark
2 gantry cranes 300 T/45 m (of
1960)
2 gantry cranes 120 T/45 m (of
1960)
Detailed appraisal of the steel structures and mechanical equipment
Technical proposals, planning, budgets
Engineering of corrective measures
Inspection and technical assistance during refurbishment activities
SWG - Grundstücks GmbH & Co. /
(Ex
AG
1 gantry crane 500 T/65 m (of
1965)
Detailed appraisal
of the crane in preparation of intended
refurbishment/modernisation
Engineering
assistance, extension of the runway
1992-94 : Chantiers de l'Atlantique / St. Nazaire / France
Aumund Kransysteme GmbH / Rheinberg /
Cegelec / Massy /
Montalev / St. Nazaire / France
Siemens
AG /
1 gantry crane 750 T/130 m (of
1968)
Detailed appraisal
of the steel structure
Technical solutions
of repairs; supervision of execution
Management concept
of total modernisation of the electrical system
Participation in
evaluation of technical proposals by alternative suppliers, in drafting of
final specification and in evaluation of tenders
Participation in
development of a new driver's cabin; definition of dismounting and erection
procedures
Engineering of
modifications of cabin suspension
Inspection and
technical assistance during erection/modification work
1995 : Ateliers et Chantiers du Havre
/ Le Havre / France
Cegelec / Massy /
Montalev /
Quillery /
1 gantry crane 500 T/65 m (of 1965)
Technical assistance in a study for transfer of this crane from
Bremen to Le Havre, including extension of span, complete
refurbishment and a new crane runway
1995-96 : Burmeister & Wain / Copenhagen / Denmark
Topdanmark
Insurance / Copenhagen / Denmark
Monberg & Thorsen / Copenhagen
/ Denmark
1 gantry crane 300 T/45 m (of 1960)
Following major accident requiring replacement of the shear leg:
Examination of consequences
Technical proposals (2 variants) of remedial work;
procedures, planning, budgeting
Technical assistance during engineering phase
Technical assistance and supervision during execution
1997 : Harland & Wolff /
2 gantry cranes 840 T/140 m (of
1969 and 1974)
Planning of a complete structural, mechanical & electrical
refurbishment
1998 : Chantiers de l'Atlantique / St.
Nazaire / France
Nelcon /
Cegelec / Massy /
1 gantry crane 750 T/130 m (of
1967)
Following major accident, management of a complete
replacement of a 2 x 250 T main
trolley; new design of
machinery house and of the trolley anchoring system
New trolley operational in 5 ½ months!
1999 : Chantiers de l'Atlantique / St.
Nazaire / France
van Seumeren / de Meern
/ Holland
Mammoet Stoof / Breda / Holland
Nelcon / Rotterdam / Holland
1 gantry
crane 450 T/125 m (of 1976)
Management of a study for transfer of the crane from
complete refurbishment
2000 : ALSTOM
Marine / Chantiers de l'Atlantique / St. Nazaire / France
Alstom Power Conversion / Massy
/
van Seumeren / de Meern
/ Holland
Mammoet Stoof /
Nelcon /
Skanska – Ralling / Malmö /
Sarens – de Coster / Wolvertem / Belgium
Noell-Reggiane / Langenhagen / Germany
Monberg & Thorsen / Copenhagen
/ Denmark
Kralovopolska / Brno / Czech Republic
1 gantry crane 1500 T/174 m
(of 1974)
Management of a study of transfer of the crane from Malmö to
St. Nazaire including shortening of span,
complete refurbishment
and a new 1010 m runway
ALSTOM
Marine / Chantiers de l'Atlantique / St. Nazaire / France
Entrepose-Montalev / St. Nazaire /
Apave /
1 gantry crane 750 T/130 m (of
1968)
Detailed survey of steel structure
Technical solutions of repairs
Preventive maintenance recommendations
Elefsis Shipyards
/ Elefsis / Greece
1 gantry crane 400 T / 58 + 27 m
(of 1973)
Detailed survey of steel structure
Technical solutions of repairs
Preventive maintenance recommendations
2001 : Dockan Exploatering
AB / Malmö / Sweden
Demotec Nordiska AB /
Norrköping / Sweden
Fagioli PSC Heavy Lift Ltd.
/ Iver /
Hebetec Engineering AG / Hindelbank / Switzerland
Krupp
Fördertechnik GmbH / Cologne / Germany
Mammoet Global BV / Rotterdam / Holland
NCC
Anlegg / Oslo / Norway
Rigging Management Systems AB / Skövde
/ Sweden
Transrig AS / Verdal / Norway
Verkehrsbau
Union GmbH / Dresden / Germany
1 gantry crane 1500 T/174 m
(of 1974)
Review, evaluation
and technical/contractual assistance in the
tender for
dismantling of the above crane
2001 - 2005 : Elefsis Shipyards / Elefsis
/
1 gantry crane 400 T/58 + 27 m
(of 1973)
Following crane survey in 2000, management, engineering and supervision
of complete rehabilitation of the steel structure
2004 : ALSTOM
Marine / Chantiers de I’Atlantique / St.Nazaire / France
1 gantry crane 1000 T/130 m
(New)
Principal consultancy in all technical subjects as well as organizational/procurement
strategies
2004 - 2005 : 3rd May Shipbuilding Industry /
(in cooperation with
Siemens AG)
1 gantry crane 300 T/104,3
m (of 1973)
Detailed
survey of structural steelwork
2005 - 2012 : STX France SA / St Nazaire / France
1 gantry crane 750 T/130 m
(of 1968)
Project
aiming at life
extension of structural steelwork:
in-depth survey, selection and
engineering of modifications
In all probability the first of its
kind in this class of cranes
Note: Project currently still in
progress.
2006 - 2008 : AIRCRAFT CARRIER Alliance (UK Ministry of Defence,
Babcock
International, British Aerospace, KBR, Thales, Vosper
Thorneycroft)
represented
by Babcock Marine / Rosyth /
1
gantry crane 1000 T/119 m (New)
Technical
consultancy from first conceptual stage up to
organizational
and procurement strategies and technical
evaluation
of tender
APPENDIX 2
SP2000/SP2000A
New Concept of 2nd Generation Heavy Gantry Cranes for
Shipyards
The existing 1st
generation of these cranes has its origins in the sixties and early seventies
when a majority of this crane "population" was designed and built.
To the knowledge available
today, no new concept appeared on the
market ever since prompted, no doubt, by adequate supply of the yards with
cranes of theoretical (= calculated) lifespan of 30 years as well as
disappearance of many original suppliers. The practical lifespan is estimated
at 40 years plus, depending on severity of loading, quality of maintenance as
well as obsolescence for other reasons, such as productivity limitations
(lifting height/capacity/reliability) and cost of maintenance.
The new concept
responds to the present and future needs of the industry by increased lifespan
and reliability, combined with sizeable reduction in operational and
maintenance cost.
Particular challenge
to the new concept lies in capacity limitations of existing runways combined
with increased height and live-load requirements to augment productivity and to
shorten construction time in dock. The concept takes every conceivable measure
in order to maintain the existing loading of the runways, thus avoiding costly
reinforcements of the civil works to the maximum possible extent. Resulting
sizeable reduction in mass is equally an asset in earthquake locations.
Further and
particular strength of the concept lies in the fact that it is based on
extensive experience gathered during numerous projects of refurbishment or
enhancement of operational life of the existing, 1st generation
cranes. The key issue is that those activities as well as development
activities of the 2nd generation are inseparably linked; the first
providing technical and operational support for the second.
As the title
indicates the concept exists in two variants with approximately 60% of
commonality of major elements.
The 1st
variant (SP2000), with intended capacity between 600 and 2000T is aimed at
large sophisticated yards for a key role there.
The 2nd
variant (SP 2000A), with intended capacity between 200 and 500T (but even
beyond, if special circumstances should warrant it) is more multirole, being
principally aimed at smaller yards, having a dual role (principal and secondary)
there. But it is equally suitable in a secondary role in shipyards of the 1st
variant or for tasks completely outside the shipbuilding industry.
Both variants (the
second partially) are currently subject of international patent proceedings.
In case of your
interest we would be pleased to discuss a full presentation and, as a further
step, indicate ways towards acquisition of such cranes.